Analytical Methods Measurement of caffeine in coffee beans with UV/vis spectrometer Abebe Belay a, * , Kassahun Ture a , Mesfin Redi b , Araya Asfaw a a Physics Department, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia b Chemistry Department, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia Received 31 December 2006; received in revised form 2 May 2007; accepted 4 October 2007 Abstract In this research work using UV/vis spectrophotometer the molar decadic absorption coefficients and transitional dipole moment of pure caffeine in water and dichloromethane were obtained at 272 and 274.7 nm. The molar decadic absorption coefficients of caffeine in water and dichloromethane at these wavelengths are 1115 and 1010 m 2 mol 1 , respectively. The calculated values for the transitional dipole moment of caffeine in water and in dichloromethane are 10.40  10 30 and 10.80  10 30 C m, respectively. After characterizing caffeine in water and dichloromethane, fast and simple methods were developed that enable to quantify the content of caffeine in coffee beans. The methods helped in extracting caffeine from coffee dissolved in water by dichloromethane, and Gaussian fit was applied to eliminate the possible interference with the caffeine spectra. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Absorbance; Caffeine; Characterization; Extraction; UV/vis spectrophotometer 1. Introduction Caffeine is found in various kinds of foods and drinks that we consume in daily life (Singh & Sahu, 2006). It causes various physiological effects such as relaxation of bronchial muscle, stimulation of the central nervous sys- tem, gastric acid secretion and dieresis Bolton and Null (1981). And their concentration in vivo is a key mark for various disorders including heart disease, carcinogenesis, kidney malfunction and asthma (Zhang, Lian, Wang, & Chen, 2005). On the other hand, chemical analysis of caf- feine in coffee beans is also used as an additional tool for evaluating coffee quality. Higher caffeine contents associ- ated with highest quality samples compared to other Ara- bic samples have been reported by Franca, Mendonca, and Oliveira (2005). Therefore, establishing a rapid and cheap analytical method for the determination of caffeine in coffee beans has an interest for a wide range of physio- logical effects on the human body and quality controls. Several chemical and physical methods have been devel- oped for the determination of caffeine in coffee and other beverages. The most widely used methods for the determi- nation of caffeine in beverages include various analytical techniques such as derivative spectrophotometer (Alpdo- gan, Karbina, & Sungur, 2002) HPLC (Branstrom & Eden- teg, 2002; Casal, Oliveira, & Ferreira, 2000; Minawlsawa, Yoshida, & Takali, 2004; Ortega-Burrales, Padilla-Wei- gand, & Molina-Diaz, 2002), Fourier Transform infrared (Bousain, Garriques, Garriges, & Guardia, 1999; Najafi, Hamid, & Afshin, 2003; Paradkar & Irudayaraj, 2002), NIR reflectance spectrometry (Chen, Zhao, Huang, Zhang, & Liu, 2006), Raman spectroscopy (Edawards, Munish, & Anstis, 2005) and capillary electrophoresis (Zhang et al., 2005), which have been reported. Although Spectropho- tometer is a fast and simple method it is not possible to determine caffeine directly in coffee beans by conventional UV absorption measurement due to the spectral overlap (Zhang et al., 2005). On the other hand, the derivative spec- trophotometer is relatively easy; however, it is not reliable for the determination of small concentration of caffeine in samples. With HPLC methods the use of expensive equip- ments and the demand for more operator attention prevent 0308-8146/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2007.10.024 * Corresponding author. Tel.: +251 911712766. E-mail address: abebealem2004@yahoo.com (A. Belay). www.elsevier.com/locate/foodchem Available online at www.sciencedirect.com Food Chemistry 108 (2008) 310–315 Food Chemistry